Natural history of the revised ALS functional rating scale and its association with survival: the PRECISION-ALS Extant Study

Objective To characterize the natural history of the revised ALS functional rating scale (ALSFRS-R) over a 24-month period following initial assessment, and to assess its associations with survival. Methods Longitudinal ALSFRS-R measurements and survival data were obtained from seven population-based, European cohorts. Different models for the ALSFRS-R trajectory were evaluated, including tests for linearity and between-cohort differences. We employed a joint modeling framework to factor in mortality, thereby aiming to derive a more precise estimate of the population’s rate of decline, while simultaneously delineating its relationship with survival. Results In total, 7,030 patients were included who produced 31,746 ALSFRS-R measurements during a follow-up period of 10,285 person-years. There was substantial evidence for a non-linear time trend within all cohorts (all p < 0.001), with faster progression rates at the beginning of follow-up. The average rate over 24 months was 0.89 points per month; 95% of the patients had a rate between 0.04 and 1.96. Overall, two components of the ALSFRS-R trajectory were found to be associated with survival: (1) the actual value of the ALSFRS-R total score and (2) the rate of change at any given time (both p < 0.001). Conclusions Functional loss in ALS follows a decelerating trajectory, where the current functional status and the rate of change have a direct impact on the patient’ s probability of survival. Given the pivotal role of the ALSFRS-R in drug development, these results help to separate treatment benefit from the disease’s natural trajectory and to estimate the impact on survival.